The neural tube is one of the earliest structures to form during vertebrate embryogenesis; it forms the scaffolding upon which the brain and spinal cord will develop, therefore, proper establishment of the neural tube is critical for normal development of the central nervous system. Pax3 encodes a DNA-binding transcription factor that is expressed early during neural tube formation and is essential for neural tube closure at the rostral and caudal neuropores, and for proper dorsalization of the alar plate. We have found that maternal diabetes inhibits expression of Pax3 in embryos of diabetic mice and increases neural tube defects (NTD). NTD are among the most common of the congenital malformations in the offspring of women with diabetes. Therefore, understanding how maternal diabetes disturbs the expression of Pax3, and how insufficient production of Pax3 leads to NTD, is important to understand how these defects occur. Recently, we showed that p53 deficiency rescues embryos with nonfunctional Pax3 alleles from NTD, and that steady state p53 protein levels are reduced in embryos expressing wild type Pax3 compared to embryos expressing nonfunctional Pax3. Based on these findings we hypothesize that Pax3 directs neural tube development by suppressing p53-dependent apoptosis by inhibiting p53 synthesis or stability. We will test this hypothesis in this proposal by determining whether Pax3 prevents cell cycle arrest and subsequent p53-dependent apoptosis in the neural folds prior to neural tube fusion, and during dorsalization of the neural tube following fusion (Aim 1), and determining whether p53 synthesis or stability is inhibited by Pax3 and investigating the mechanisms by which impaired synthesis or stability of p53 occurs (Aim 2). Aim 1 will be performed using knockout mouse lines, in which the Pax3 gene has been tagged with a reporter gene so that Pax3- expressing cells can be fate mapped during neural tube formation, that have been crossed with p53 knockout mice. Aim 2 will be performed using cells lines that express Pax3 or not, and p53 to study p53 synthesis or stability. This research will significantly advance our knowledge of how closure and dorsalization of the neural tube is regulated, and provide new information on the molecular mechanisms by which diabetic pregnancy causes NTD.